The present invention relates to an improved process and apparatus for statically mixing layers of separate fluid components. More particularly, the present invention relates to improvements in such static mixing by use of mixers of the interfacial surface generator type.
The use of static or motionless mixers of the interfacial surface generator type is well known for the mixing of two or more streams of fluids, particularly viscous liquids, whereby the fluids are driven in proportion through an interfacial surface generator which mixes the fluids. This mixing is achieved by division of an inlet fluid stream containing layers of each of the fluids into a plurality of substreams, then reorienting and recombining the substreams into a main stream, and then repeating such division, reorientation and recombination until a desired degree of mixing of the fluid components is achieved.
Examples of such static or motionless mixer systems of the interfacial surface generator type are shown in U.S. Pat. No. 3,182,965, No. 3,195,865, No. 3,286,992, No. 3,394,924, No. 3,404,869, No. 3,406,947, No. 3,424,437 and No. 3,583,678. Such known static or motionless mixers have greater simplicity, almost zero heat input, and have no moving parts, as compared to more conventional dynamic mechanical mixers.
Such static mixers were originally developed for the "in-line" mixing of chemicals where continuous flow maintains the desired proportion of the components taken at any cross-sectional area of the mixer, and such mixers are conventionally designed to maintain such given proportion throughout the mixer.
However, such continuous and proportional operation is very difficult to achieve under actual operating conditions. That is, it is difficult to actually achieve completely continuous flow of all components to the inlet of an interfacial surface generator. Rather, what normally occurs is that the supply of one of the components will be temporarily interrupted, with the result that the stream which is supplied to the interfacial surface generator includes periodic solid patches or spots of only one of the components. Such discontinuous supply may be caused due to the pulsation of the pumps employed to supply the components. Such discontinuous supply is unavoidable when the components are supplied when discharging shot volumes, due to "preflow" or to "afterflow" inherent in such supplying operations. Such preflow or afterflow may occur due to differences in compressibility of the two components, since most liquids will contain some amount of entrained air, thus making the liquids nonhydrostatic. Such preflow or afterflow is also likely to occur due to the fact that the two components are normally supplied by flexible hoses, and some degree of expansion and contraction of such hoses is unavoidable.
Accordingly, in the practical application of a static mixer of the interfacial surface generator type, it is often impossible to supply plural components to the interfacial surface generator without some interruption in the continuity of flow of the plural components. Unfortunately, this interruption of continuous flow is transmitted throughout the entire mixing operation of a conventional static mixer. The result is that there will be discharged from the mixer an outlet stream including a mixture of the fluid components, but such mixture will have therein solid patches or spots of the component corresponding to the initial patches or spots in the inlet stream. In other words, the solid patches will be passed entirely through the conventional static mixer and will appear in the finished product. Accordingly, in spite of the numerous potential advantages of static mixers of the interfacial surface generator type, the precise nature of such mixers, i.e. the maintenance throughout the mixer of predetermined fluid proportions, results in faults in the supply of the fluids being transmitted through the mixer and appearing in the finished product.
Such faults are unacceptable in many finished products. Thus, to eliminate such faults in operations which include the mixing of reactive multi-component materials, such as epoxies, polyesters, polyurethanes, silicones, etc., it has been necessary for industry to employ the use of dynamic mechanical mixers, which by their very nature will disperse solid patches of a single component. As indicated above however, conventional dynamic mechanical mixers have certain inherent cost and operational disadvantages, and it would still be desirable to industry to have a static mixer of the interfacial surface generator type which would avoid the above discussed faults occurring in the finished product, even when the component supply to the mixer is not ideally continuous.